Dyeing of leather



' veloped on the leather to Patented May 17, 1938 John Bur-chill,

assignor to Imperi Blackley, Manchester, England,

al Chemical industries Limited, a corporation of Great Britain No Drawing. Application February 1, 1937, Se- I rial No. 123,545. In Great Britain January 30,

1 Claim.

This invention relates to new colored leathers,

and especially toleathers which are dyed with a class of leuco vat dyestufis and to processes of dyeing leathers.

Dyeings on leather which are-fast improved to wash ing, moreespecially the dyeings on glove leather, have been obtainable generally only in pale or dull shades, such as dyeings produced by sulphur Bright shades on leather which have dyestuffs.

been produced were not entirely satisfactory from the'standpoint of fastness to washing, such as' leathers dyed with the acid or direct colors. For'example, it has hitherto been found impossible to obtain bright reds, oranges, blues and greens, especially on glove leather which had good light fastness and would withstand reasonable washing treatment.

It is among the objects of provide dyed leathers the invention to in bright shades which have good fastness to washing and light. Another object is to provide improved processes for dyeing leathers. Other objects of the will be apparent from the following tailed description of the invention.

invention more de- The objects of the-invention are attained by applying to leather, such as aldehyde-tanned chamois and other washable leathers to which leathers the invention lends particular value, compounds which are sulphuric, esters of leuco vat dyestuffs and these compounds are thendethe vast dyestuifs themselves, whereupon the dyed leathers may be finished by fat liquoring preceded, if desired, by soaping treatment. By means of my invention shades may be produced on-leather of a fastness to washing and light hitherto unattainable. The

' leuco vat. dyestufi sulphuric esters may be conveniently applied according to the invention and particularly illustrated in the invention is more the following examples which are illustrative and not, limitative of the invention.

- Example I lbs. of aldehyde dressed sheepskin splits were washedby drummingior 5 minutes in warm 1 water, rinsed and then immersed in 30 gallons of water at 35 C. i'n the drum. After rotating for a few minutes, 5'lbs. of the leuco sulphuric ester of thedyestufi v zanthrone (Color Index 1101), solved in 3 gallons of water at 50 and after a further'20 minutes-1V known as dimethoxydibenpreviously dis- -C.' were added lbs.

of glacial acetic acid diluted with twice the volume of water was introduced I of the next 15 minutes and drumming gradually during the course continued were further treated as in Example 1.

Example 11 50 lbs. of chamois leather were stripped and wetted back with warm water in which was dissolved lb. soda ash, rinsed and immersed in 30 gallons of water at 35 C. in the drum. 5 lbs. of the leuco sulphuric ester of the dyestufi known as 5:5'-dichloro-6:6'-dimethyl-2:2'-bisthionaphthene indigo (Color Index 1212) dissolved in 10 gallons of water were added and after i ,20 minutes agitation, 3 lbs. of glacial acetic acid diluted with 2 quarts of water were added slowly, dyeing being completed in a further 30 minutes. The exhausted dye liquor was then run of! and the skins refioated in a 1% aqueous sulphuric acid solution at 20 C. to which 1 lbs. sodium nitrite were added. After 5 minutes the skins Example III Leukanol stained chrome tanned cabretta glove leather was wet out with-a dilute ammonia solution, the treatment bei carried on for 30 minutes at 102 F. After ashing and striking out excess water a 5% solution of 'a mixture of equal parts of formic and'sulphuric. acid was brushed on the grain side to prevent undue penetration of the dyestuif and the excess water was struck out. 'A 2% aqueous solution of -Ponsol jade green soluble was brushed on, and followed immediately by a 1% aqueous solution of sodium nitrite. The surface was then washed with a liberal flow of fresh water at F. followed 45 by-tumbling for 5 minutes. Finally it wasfat liquored with s'ulphonated neats-foot oil.

The dyeing was of a full bright-shade having much better fastness to washing than dyeings obtainable with water solutions of acid, direct, chrome or basic dyestuifs. The leather was col ored only on one side and there was no undue penetration of the dyestufi', such as that which is undesirable on leather for women's gloves.

' leather which was prepared for dyeing in the same manner.

Example IV The dyes used in accordance with Example III were used to dye Leukanol stained chrome tanned cabretta glove leather in the drum. The leather was wet out for 30 minutes at 102 F. with 2% ammonia solution, then 5% by weight of the dyestuif was added and the leather was run in the drum for 30 minutes. 2 of formic acid and 2 of sulphuric acid were then added, and after 5 minutes sodium nitrite to make the solution up to 2% was added, and run for 20 minutes. After washing the stock was fat liquored with sulphonated neats-foot oil and was found to be dyed medium shades of green and blue accordingly as the green or blue dye was used. The dveings had good fastness to washing and compared favorably with the results obtained by brush treatment as illustrated in Example III.

Similar results were obtained when similar treatment was applied to sumac stained chrome tanned cabretta glove leather.

As illustrative of other suitable coloring matters of the kind which can be used according to the invention as illustrated are the leuco sulphuric esters of the dyestuffs known as fiavanthrone (Color Index 1118) dichloroisodibenzanthrone (Color Index 1104) 5:7:5':7'-tetrabromindigotin (Color Index ,1184), trichloro-N-dihydro- 1:2:1:2'-anthraquinoneazine. The most of the leucoesters of vat dyestuffs which are used 'in ac- 2,117,699 treatment when "Ponsol Blue BF Soluble was cordance with the invention are of excellent fastness to light and all are of very good fastness to Washing.

In certain cases, as exemplified, for instance. in

-Example I, itis advisable to add the acid gradually to the dye bath to promote greater levelness of shade. The degree of penetration into the leather may be regulated by increasing or diminishing the time of dyeing previous to adding the acid. Development may be carried out in the exhausted dye liquor or in a fresh solution and other developingagents, for instance, ammonium persulphate in dilute mineral acid, may be employed in place of acidified nitrite.

Incorporation of soap up to 2 parts per 1000 in the fat liquor or separate soaping in a similar strength solution at C. may be employed, if desired, to give brighter shades and better fastness to rubbing.

As still other modifications of the invention will be suggested to those skilled in the art without departing from the spirit and scope of the invention, it is .to be understood that no limitations are intended other than those which are specifically expressed in the appended claims or are imposed by the prior art.

Still other types of leather e. g. paddles, may be used.

I claim:

The process which comprises dyeing at least an outer layer of a wet-out leather with an aqueous solution of the sulphuric ester of a leuco vat dyestuif, gradually acidifying with a dilute acid and there developing the color by applying a dilute acidified solution of an oxidizing agent, the temperature of said saturating, acidifying and development not exceeding 50 C.

JOHN BURCHILL.

dyeing machinery, 

